This invention relates in general to telemetry systems and is more particularly directed to systems with a daisy chain of data ports. A daisy chain of data ports is a chain of serially-connected data ports, wherein a signal is passed from port to the next in serial fashion.
Among other uses, telemetry systems commonly are used to transfer data from a plurality of equipment monitors and to transfer data to a plurality of equipment controls. Telemetry systems for tranferring data from and to transmitters and receivers to and from a plurality of equipment controls and monitors are made in many configurations for various specific uses. Among the parameters determining which telemetry system configuration is utilized are access time, simplicity of use and cost. Because the cost of transmission lines can be considerable, particularly where long distances between the transmitter or receiver and the equipment controls or monitors are involved, daisy-chain systems utilizing only one output data line and/or one input data line are desirable. Such a system is described in U.S. Patent Application Ser. No. 428,545 by Herbert Alan Schwan filed Sept. 30, 1982 for "TELEMETRY SYSTEM FOR DISTRIBUTED EQUIPMENT CONTROLS AND EQUIPMENT MONITORS". In such system, data ports coupled to the controls and monitors are attached to the respective output or input data line serially as shift register stages. The output data from the transmitter is shifted down the output data line with each shift being clocked by a clock pulse, until the data reaches the shift register stage (data ports) for the last equipment control. At that time a clock frame pulse simultaneously enables all of the shift register stages (data ports) to transfer their instant data to their respective equipment controls. Input data is shifted up the input data line to the receiver in the same manner from data ports that are coupled to the equipment monitors and which are connected to each other in series to function as stages of a shift register.